The field of the disclosure relates generally to a motor controller for electric blower motors and, more specifically, a motor controller that enables approximately constant airflow production.
At least some electric motors are torque-calibrated when manufactured to ensure the torque output at the drive shaft of the electric motor matches the torque commanded. At least some electric motors, particularly electric motors driving blowers, such as a forward curve blower, are further calibrated to produce approximately a constant airflow during operation in either a torque-control mode or a speed-control mode. Such a calibration, or characterization, quantizes airflow output for a given speed and torque output when driving the blower. The actual airflow output can vary according to the blower construction, duct or other airflow restriction into which the airflow is directed.
Constant airflow heating, ventilation, and air conditioning (HVAC) systems improve thermal comfort and energy savings. Constant airflow systems may also be used in certain refrigeration systems. In a constant airflow system, a motor controller for an electric blower motor receives an airflow rate demand, e.g., a value in cubic feet per minute (CFM), and then determines, e.g., by a polynomial or constant airflow algorithm, an appropriate motor torque or motor speed to produce approximately the airflow demanded. In a torque-controlled implementation, for example, motor torque is regulated based on a monitored motor speed to produce the approximate airflow. The estimation of actual airflow produced for a given motor torque and motor speed is subject to various sources of error, including, for example, parasitic current and noise in current sensing and current regulation circuits, magnetic flux changes with temperature, effects of magnetic flux on average current during peak current regulation, variability in bearing friction, variation and drift in calibration procedures and equipment, and imperfections in drive torque production linearity. Further, errors in estimates of actual airflow may be introduced by differences in air density, for example, in high altitude regions, where the constant airflow system is installed versus where the blower is characterized, e.g., low altitude regions. A motor controller that compensates for air density changes in its torque-speed-airflow relationships is desired.